Hi:Pete Gruendeman, long time EDM operator here. I have also written EDM
software which went forward, backward and escaped sideways off the program path.
EDM motion is based on either:Positioning, at whatever rate you program though
it's typically rather slow;or
Erosion, with no feedrate what so ever. Sparks radiate from the wire or
carbon/copper electrode in all directions, eroding the workpiece where those
sparks make contact. Motion forward in the programmed path is all about
maintaining erosion gap voltage, and possibly current, within limits which is
controlled entirely by movement of the electrode. Don't call it a feedrate
because It's not a feedrate.
Read the gap voltage;If/ gap voltage > 3/4 Voc, move ahead;If/ gap voltage >
3/4 Voc && < 2/3 Voc, stay put;If/ gap voltage < 2/3 Voc, backup;repeat
All of this start, stop, backup motion will result in an average rate of travel
that is on the order of inches per hour. It's not fast. Though the
positioning rate for forward and reverse motion can be inches per minute.
What's really needed for useful EDM control is all of the above plus backing up
on or escaping off the programmed path at timed intervals or based on erosion
conditions. It's not that hard to write as I have already done it in four axis
moves, linear interpolation only, no wire diameter compensation. Code or ideas
sent upon request.
Pete Gruendeman
On Friday, February 26, 2016 7:10 AM, Nicklas Karlsson
<nicklas.karlsso...@gmail.com> wrote:
I understand flushing is important but nothing about how ot adapt speed.
> On Friday 26 February 2016 05:07:20 Nicklas Karlsson wrote:
>
> > > >Anybody familiar with EDM who could tell me how to adjust the feed
> > > > rate for EDM operations?
> > >
> > > Not a very trivial task but it can be done. There is a youtube video
> > > showing and EDM running on linuxcnc. Do a search. The problem comes
> > > in when you have to backup as some EDM machines do.
> >
> > Programming I could solve. Then controlling speed and backup what do
> > they try to achieve: A certain average gap voltage? Ignition voltage?
> > Power in each pulse?
> >
> I have only used edm 3 times, in each case in blind holes. The first time
> I drove it by hand from the arrow keys, but found the blind holes lack
> of the electrolite fluid circulation to be a major problem as the juice
> in the hole would gradually get conductive & short it out. I did get the
> first broken tap removed but it was an all day job. I found also that
> if the electrode was rotating at 50 to 100 revs, that induced
> circulation seems to help. So I wrote a loop that drove it to a fixed
> very small increment farther each time, doing g0 moves so the
> electrolite was somewhat pumped in and out of the hole, and the second
> busted tap was cut out in about 1/3rd of the time. But I felt the power
> supply was a bit puny, so the next time I traded the 2uf capacitor out
> for a 10 uf (both oil filled paper caps) and doubled the voltage to
> around 75 volts while reducing the resistor from 50 ohms to 25, lots
> more power per pulse.
>
> Later, needing mounting holes in a 10" carbide tipped saw blade so I
> could mount it on a rotary table to sharpen it, I used hollow brass
> tubing as the electrode, rotating in the mills chuck to help circulate
> the juice. With more power it was faster, but even with 29db shooting
> earmuffs on, the noise was still in the 130 db area and a bit painfull.
> That saw blade made a great sounding board and I expect it could be
> easily heard 3 to 6 blocks away. It also drilled the cleanest holes I
> have ever seen in that hard chrome plated steel.
>
> So the importance of being able to circulate the juice to keep the
> metalic debris flushed from the working area is at last as important as
> the height control. As for active height control, one might be able to
> use one of the thc modules for that but I've not tried it.
>
> With very short, heavy leads between the capacitor and the workface, a
> diode to rectify the peak voltage reached at the capcitor would seem to
> be the measurement method of choice, but that, even with very short
> leads, might need some r/c filtering because the discharge IS going to
> induce some resonant ringing, likely sufficient to cause micro-arcing in
> a common bulk carbon resistor, which will manifest itself as an initial
> lowering of the filtering resistors measured resistance, and a drift in
> the desired operating voltage until the resistor is destroyed. For the
> same reason, the diode needs to be a very fast recovery diode and rated
> at least to 1 kilovolt.
>
> Not hugely helpfull Nicklas, but that is what I learned based on 65+
> years of making electrons do useful work.
>
> > Nicklas Karlsson
> >
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>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
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